JP 2652788 B proposes a conventional power steering device for a boat with an outboard motor in which power-assisting is effected by an electric motor.
In the above-mentioned conventional device, the operation of the steering wheel arranged at the driver's seat is transmitted through a wire to an outboard motor with an engine steerably supported at the rear of the boat, and the outboard device is rotated in correspondence with the steering amount of the steering wheel. Further, there is provided a power assist mechanism by means of which the torque of an electric motor causes the outboard motor to rotate through a speed reduction gear. An electronic control unit (ECU) controls the assisting force of the electric motor in correspondence with a steering torque signal of a torque sensor for sensing steering torque from a steering force acting on the wire portion, an engine RPM signal of the outboard motor, etc.
However, in the above-described conventional device, in which the electric motor and the torque sensor are arranged in the vicinity of the engine of the outboard motor, it is necessary to achieve an improvement in waterproofness so as to prevent intrusion of water scattered from the propeller, etc., resulting in an increase in product cost.
Further, due to the use of the steering torque sensor for sensing the operating force of the wire through which the outboard motor is pushed and pulled by operating the steering wheel, the steering torque that can be sensed is reduced due to friction of the wire generated in steering, with the result that the assisting force is suppressed, which leads to a limitation to a reduction in the requisite steering force.
The present invention has been made in view of the above problems in the prior art. It is an object of the present invention to provide a power steering device for a boat in which there is no need to take waterproofness into consideration and which allows easy drive with small steering force.